Reconstituted collagen is widely used in the manufacture of tubular sausage casings. These sausage casings are edible and relatively easy to masticate or chew. A highly desirable characteristic of such casing is the translucency of the casing which allows the meat color to be perceived through the casing. Reconstituted collagen casings have a tendency to absorb water from the meat emulsion. This absorbed water hydrates the casing, and the casing becomes opaque, thereby blocking the transmission of meat colors through the casing. In order to prevent the hydration of the casing, some processes use extensive chemical crosslinking agents which make the collagen less hydratable. Although such chemically crosslinked casing has improved translucency properties, the extensive crosslinking of the collagen makes the casing less tender and difficult to chew and, therefore, less desirable as a sausage casing.
The prior art processes provide casings which have good translucency but which are difficult to chew and casings which are tender and relatively easy to chew but which have poor translucency properties.
The present invention provides a process which significantly improves the translucency of the casing without leading to excessive toughness of the casing. The present process employs materials which have long been used in the manufacture of reconstituted collagen casings and, thus, offer a minimum number of problems in connection with toxicity, and these materials have all been approved for use in the food processing of various foodstuffs.
In conventional sausage casing processes, the raw collagen used in the manufacture of the casing is derived from corium layer of a cowhide. The hides are usually processed to dehair the hide and to deflesh the hide and then chemically treated to remove non-collagen protein and other materials from the hide. The hide is then split to remove the epidermis. All these processing steps are usually carried out on standard tannery equipment. The hide is then usually cut into small sections, from 1/2 to 4 square inches, and reduced to a pulp by passing it through grinders. The finely ground hide is then usually swollen with acid and blended with other ingredients in a suitable homogenizer to make an extrudable gel. In the present process, the corium layer of the hides is treated prior to the hide being cut into pieces. The treated hide corium can be refrigerated and held until needed.
The process of the present invention includes the treatment of the hide corium with a solution containing hydrogen peroxide, glycerine and a ferrous salt. This treatment results in a casing which has a significantly improved clarity over a casing prepared from the same hides that have not been subjected to the treatment of the present process.
Hydrogen peroxide has been previously employed in the treatment of collagen for use in food, cosmetic and pharmaceutical applications. The hydrogen peroxide has been used as a bleaching agent and to remove objectionable odor and flavor properties in the collagen material. Examples of the use of hydrogen peroxide for this purpose can be found in U.S. Pat. Nos. 2,928,822 and 3,308,113. Hydrogen peroxide has also been employed as an agent to modify the collagen to make it more readily dispersible in water. An example of this process can be found in U.S. Pat. No. 3,073,702. In addition to the above, there are a number of collagen preparation processes which employ an enzyme to break down the non-collagen proteinaceous materials in the hide. In these processes, hydrogen peroxide is often used to limit the effect of the enzyme.
The hydrogen peroxide is present in the solution used in the process of this invention in an amount of from 0.5% to 3% by weight of the aqueous solution. Less than 0.5% of hydrogen peroxide in the solution does not provide the desired results in a reasonable time period. More than 3% hydrogen peroxide in the solution does not offer any advantage in the process.
Glycerine is commonly used in the manufacture of collagen casing as an plasticizer. Generally, the extruded tubular casing is passed through a bath containing glycerine before the casing is dried. U.S. Pat. Nos. 3,408,917; 3,535,125; 3,512,997 and 3,567,467 disclose the use of glycerine as a plasticizer in the manufacture of collagen casing. In the present process, the glycerine is added to the corium hide layer at a much earlier stage in this manufacturing process, and at this point in the process it does not function as a plasticizer.
The third ingredient in the solution used in the present process, a ferrous salt, has been used in collagen processes as an ingredient in a tanning solution. The tanning of the casing occurs after the casing has been extruded. The function of the ferrous iron of the present process is not to tan the hide, as tanning the hide before the preparation of the gel would prevent the gel from forming a cohered, tubular casing. The ferrous ion is added to the solution in the form of ferrous chloride (FeCl.sub.2 --4H.sub.2 O) or ferrous sulfate (FeSO.sub.4). The ferrous chloride is preferred because it is more soluble in the water. The ferrous ion is added in sufficient quantity to give a concentration of from 25 to 70 ppm. of ferrous ion in the treating solution with 45 ppm. being preferred. Concentrations higher than 70 ppm. have a tendency to discolor the casing.
Generally, the present process consists of treating the buffered corium layer of hide with a solution containing hydrogen peroxide, glycerine and a ferrous ion, preferably ferrous chloride, for from approximately 3 to 16 hours prior to the hide being comminuted and processed to form a gel. The solution which is used to treat the hide generally contains approximately 0.5% to 3% hydrogen peroxide, preferably 1% of hydrogen peroxide, from 2% to 5% glycerine, preferably 3% glycerine and 25 parts per million to 70 parts per million of iron from salts such as ferrous sulfate or ferrous chloride, preferably 45 ppm. The hide corium is treated with a solution for a minimum of about 3 hours while the hides are constantly being agitated in the solution. It is preferable to use a rotating treatment vessel to contact the hides with the solution, although other types of agitating systems may be employed. The preferred ratio of the peroxide to glycerine to ferrous chloride ingredients in the solution is 1:3:0.016. With this ratio of ingredients in the solution, the desired results can be achieved with a contact time of three hours. The weight ratio of the treating solution to the hide is from 1 to 2 parts of solution to 1 part of hide, 1-2:1.
The contact of the hides with the solution in the present process can be performed by adding the hides to the solution, adding the preformed solution to the hides or by adding the ingredients of the solution to a vessel containing the hides. If the ingredients are added to a vessel containing the hides, it is necessary to add the glycerine to the hides prior to the addition of the hydrogen peroxide. If the hydrogen peroxide is added to the hides first, it rapidly decomposes.
The mechanism by which the present process increases the clarity of the casing produced from the treated hides is not understood. As it is known that glycerine and hydrogen peroxide can react to produce glyceraldehyde, it was postulated that the clarity effect was due to chemical crosslinking of collagen by glyceraldehyde. However, the direct additon of glyceraldehyde to the hide at the same point in the process did not produce the casing clarity produced by the present process.
It should be understood that the clarity treatment process of the present invention can be employed with other processes, e.g., chemical crosslinking, to produce casings with even greater clarity or translucency.
The measurements of clarity or translucency are performed on a M-500-A Agtron Direct Reading Reflectance Spectrophotometer. This unit is manufactured by Magnuson, Inc. The Agtron Spectrophotometer consists of two light sources which are gaseous discharge tubes for illuminating the sample. There are interference filters for selecting one of four monochromatic lines from the sources. It has been determined that the present casings normally give the most meaningful results when tested on the Agtron with the blue color mode. In conducting the test, a M-300-A sample holder and light source is used in conjunction with the M-500-A primary unit. Casings made by the various examples in the present application are filled with warm water at a temperature from 70.degree. F. to 80.degree. F., and the ends of the casings are tied. The casing length is usually about 4". The diameter of the water-filled casing is typically the same as when filled with a meat emulsion. A number of casings are set in the sample cup. Usually about 7 casings are sufficient to fill the cup. The Model M-300-A sample holder includes a mask which covers only the central region of the casings so that the entire mask is filled with casing material. The unit is calibrated before the tests are commenced. The calibration procedure includes the following steps:
1. The instrument is turned on with the color mode selector on the blue mode and allowed to warm up for approximately 30 minutes.
2. The sample cup is placed over the viewing area, and the calibration disc 00 is inserted into the unit.
3. The zero control is set for a meter reading of "zero".
4. The calibration disc 00 is replaced with calibration disc 44.
5. The standardized control is set to obtain a meter reading of "100".
The samples are then placed in the sample cup assuring that the entire viewing area exposed by the mask is completely filled with water containing sausage casing links. The calibration disc 00 is then placed over the water filled links in the sample cup and the instrument reading is obtained.
The process of the present invention results in a reduction in the Agtron reading of the casing of from 10 to about 20 units. The reduction in the Agtron reading is not constant because of the difference in the characteristics or quality of the hides that are employed. A reduction in the Agtron value of 10 is a significant improvement in the clarity or translucency of the finished casing.